The present invention relates to a small-type optical scanner device having a photo-detector unit capable of accurately detecting a position of a light spot.
Conventionally, a confocal probe device having an optical scanner unit and a confocal optical system has been known. The optical scanner unit can cast irradiation light (for example, laser light) emitted from a light source onto an observation object and is adapted to scan the observation object by being driven by a drivable optical fiber and an electrostatically-actuated mirror. The confocal optical system receives the light scanned and reflected on a focal plane of the observation object and eventually generates a confocal image of the observation object based on the reflected light. Further, the confocal probe device detects a position of a light spot of the emitted light on the observation object so that a spot on the observation object on which the emitted light is to be cast is controlled based on the actually detected result. A following method has been known conventionally as a method to detect the spot to cast the emitted light.
FIG. 6 shows such a conventional optical scanner device 300 having an electrostaticaly-actuated mirror as a means for casting irradiation light onto an observation object 315. The optical scanner device 300 is provided with a mirror unit 302 and an objective lens system 305. The irradiation light 311 (laser light) is reflected on the mirror unit 302 and enters the objective lens system 305. The irradiation light 311 entering the mirror unit 302 is a parallel pencil, which is focused on the observation object 315. (In FIG. 6, a light spot 317 indicates the focal point.)
The mirror unit 302 includes a base plate, which is not shown, on a side of a mirror surface in the mirror unit 302 which is opposite to a side receiving the irradiation light 311, and drive electrodes are provided on the base plate. By applying voltage to arbitrary electrodes, electrostatic force is generated between the drive electrodes and the mirror so that a part of the mirror is attracted by the drive electrodes, and the mirror surface of the mirror unit 302 is arbitrarily angled. As the electric capacitance being stored in the drive electrodes when the voltage is applied and an inclination angle of the mirror are approximately linearly-related, the angle of the mirror surface can be defined by the electric capacitance stored in the drive electrodes. Therefore, a position coordinate of the light spot 317 on the observation object 315 can be calculated based on the electric capacitance. An example of such a typical mirror unit which can be electrostatically actuated is disclosed in Japanese Patent Provisional Publication No. 2003-29172.
In the optical scanner device 300 disclosed in the above publication, as the inclination angle of the mirror surface in the mirror unit 302 increases, the relation between the electric capacitance and the inclination angle of the mirror surface becomes nonlinear, thus the inclination angle of the mirror surface cannot be obtained accurately. As a result, a position wherein a control unit of the optical scanner device 300 recognizes the light spot 317 should be (which is referred to as a target position) and a position of the actually controlled light spot 317 are separated as the inclination angle of the mirror surface increases. Therefore, a problem occurs as such the image generated based on reflection which is not accurately controlled is distorted when the inclination angle of the mirror surface is greater.
In consideration of the above problem, in order to obtain an image without being distorted, it is required to measure the position of the light spot more stably rather than depending on the inclination angle of the mirror unit. Conventionally, a following method has been known as a method to measure the position of the light spot independently from the inclination angle of the mirror unit.
FIG. 7 shows a conventional optical scanner device 400 to measure a position of a light spot independently from the inclination angle of the mirror unit. The optical scanner device 400 is provided with an optical fiber 401, an objective lens system 405, a beam splitter 407, a photo-detector element 409 (for example, a photodiode). The optical fiber 401 includes a scanner unit 403. It should be noted that the optical fiber 401 can be driven in arbitrary directions by external force to scan the irradiation light 411 and is exchangeable with a mirror unit such as one described above as the mirror unit 302.
The scanner unit 403 is driven by a driving means which is not shown to cast irradiated light 411. The irradiated light 411 is emitted from the scanner unit 403 to the objective lens system 405. The irradiated light 411 transmitted through the objective lens system 405 injects into the beam splitter 407, whereby a part of the irradiated light 411 is split and angled at 90 degrees with respect to the direction of travel to enter the photo-detector element 409. An optical axis of the part of the irradiation light 411′ split from the original irradiation light 411 is referred to as an optical axis 413′. The remaining part of the irradiated light 411 advances straight to reach an observation object 415.
With this configuration, an XYZ coordinate system and its original point O are defined on the observation object 415 as shown in FIG. 7. That is, an intersecting point of an optical axis 413 and a predetermined position of the observation object 415 is defined to be the original point O, and a direction parallel to the optical axis 413 is defined to be an direction of a Z axis. An X axis and a Y axis are perpendicular to each other and to the Z axis. Further, a corresponding coordinate system with an X′ axis, a Y′ axis, and a Z′ axis and an original point O′ is defined. That is, an intersecting point of an optical axis 413′ and (an incident surface of) the photo-detector element 409 is defined to be the original point O′, and a direction parallel to the optical axis 413 is defined to be a direction of the Z′ axis. The X′ axis and the Y′ axis are perpendicular to each other and to the Z′ axis.
A position coordinate (X, Y) of the light spot 417 on the observation object 415 with respect to the original point O can be obtained by detecting a position coordinate (X′, Y′) of the light spot 417′ on the photo-detector element 409 with respect to the original point O′. Thus, a position of the light spot can be measured independently from an inclination angle of a mirror unit.
However, in the optical scanner device 400, the irradiation light 411′ split by the beam splitter 407 is received in a position separated from the original optical axis 413, therefore, a size of the device itself tends to be larger to include the photo-detector element 409 and other accompanying components. Thus, in a small space such as inside a front end portion of a probe, a smaller optical scanning device capable of detecting an accurate position of the light spot has been demanded.